The inadequacies of mechanical analog type meters, particularly with regard to indication of instantaneous peak audio level values as displayed on conventional VU meters, are discussed as background to U.S. Pat. No. 4,528,501, DUAL LOUDNESS METER AND METHOD, to Dorrough et al., which discloses an audio level monitoring and metering instrument including a relatively fast changing peak amplitude dot/bar graph type LED display and associated processing circuitry, which effectively simulates the display function of a mechanical analog meter but which overcomes the inherent ballistic limitations of mechanical meters, providing a graphic display of increased validity and utility.
In video monitoring and display there are a number of additional requirements beyond those of audio. There are a number of video parameters of interest, relating to geometric waveform relationships according to the specifications of a particular video format such as NTSC, which are inherently quasi-static in nature and, in an ideal system, would remain constant in the absence of drift, operator error, or malfunctions introducing anomalous parameter variances. Display of such parameters typically does not require fast response in the display device and thus may be performed adequately by a variety of well known amplitude display media such as switched alphanumeric LED or LCD panels or even mechanical analog meters. Those of the video parameters which are dynamic and thus impose special requirements on the speed of the display for monitoring fluctuating peak and average levels, somewhat comparable to monitoring of audio levels, relate particularly to rapidly changing instantaneous shifts of luminance and chrominance levels, for example peak excursions of the luminance level in both directions, i.e. toward white and toward black. Average picture signal levels are also of interest, and change rapidly. Due to the much higher frequency range of video, in the MHz region compared to the KHz audio region, the required display response speed is well beyond the capability of mechanical analog meters or alphanumeric readouts; these parameters are most often viewed on high speed waveform monitors, typically CRT oscilloscopes. Such video waveform monitors are usually fitted with suitable graticules to additionally enable measurement and monitoring of the abovementioned slow-changing static parameters, and may eliminate the need for separate meters. However, sufficiently accurate waveform monitors are bulky and expensive, due to the special requirements such as display linearity, high stability and wide bandwidth. Furthermore, their calibration procedures tend to be complex and the indirect manner of data presentation generally requires interpretation by trained technical operators. For these reasons, the use of waveform monitors has been generally limited to larger production locations such as professional studios, broadcast stations and laboratories.
The present invention addresses an unfulfilled need for new monitoring and display techniques and related apparatus which is less bulky, less costly and easy to operate by unskilled personnel, and thus more suited for use with portable video cameras than such apparatus of known art.